1. Field of the Invention
The invention relates to a sub-lance installation for carrying out measurements and/or taking samples in a metallurgical furnace, comprising an elongate tubular lance which is rotatable around its longitudinal axis and which is attached at its upper end to a carriage by which the lance with its longitudinal axis vertical is moved vertically to bring its lower end to an operational location for measurement and/or sample-taking.
The invention will be described in particular for application in a steel converter of the type in which liquid pig iron is made into steel by blowing in oxygen from above through a main lance onto the pig iron bath, but the invention is not limited to this application. Applications of the invention are possible in metallurgical processes in other types of metallurgical furnace.
2. Description of the Prior Art
In order to be able to monitor and control as necessary the progress of the refining process in the steel furnace during the oxygen blowing, use is often made of a sub-lance. During the oxygen blowing, or during an interval in the oxygen blowing, the sub-lance is moved downwards parallel to the main lance, until a probe carried by the sub-lance, extends into the bath. The probe can be equipped for example with means for measuring the bath temperature and/or for analysing the concentration of particular elements such as carbon or oxygen in the bath. The results of this measurement can then be passed from the probe via a cable through the sub-lance to a point outside the furnace. It is also possible to use a probe in the form of a sampling pot, in which case the sub-lance can extract a sample from the bath, which can then be analysed outside the furnace.
The use of sub-lances for carrying out measurements and/or for taking samples has been described in detail in the literature. Some examples are given below.
One difficulty arising in the use of a sub-lance is that the sub-lance, when it is near the blowing lance, is heated by the furnace asymmetrically. This causes distortion of the sub-lance with the result that it is only suitable for a few measurements. A customary method of overcoming this difficulty is to remove the sub-lance from its suspension after use and straighten it elsewhere. After this it an be suspended again and used for a subsequent operation. It is obvious that for this reason the effectiveness of the sub-lance is limited and that its operation and preparation involve much work. In particular, if the sub-lance is of the liquid cooled type, it is necessary when straightening it that the connections for liquid cooling be first removed and then fitted back in place.
A sub-lance, in which the difficulty just described is avoided, is known for example from U.S. Pat. No. 4,438,653 in which the sub-lance is rotatable about its vertical longitudinal axis. This makes it possible, after the sub-lance has been used and consequently been distorted, to rotate the sub-lance. In the next operation using the sub-lance it will bend back again to its original straight condition and then distort again, after with the sub-lance can be rotated once again. In this particular known sub-lance the rotation is done by hand using a special spanner. The difficulty of this is that in practice the rotation is often forgotten and that the spanner can be mislaid. The rotation is in any case labour-intensive and difficult to combine with a production function.
Another arrangement for the rotation of the sub-lance is shown in U.S. Pat. No. 4,141,249, wherein means for rotating the sub-lance are used, which comprise a driving motor and gear wheels. The difficulty of this arrangement is that, when rotating the sub-lance, large eccentric forces are applied to the sub-lance so that there is a danger of the cooling water connections of the sub-lance leaking. The drive, which rises and falls with the sub-lance and which has to have power supplied from the outside forms a rather complicated and vulnerable entity liable to failure under the operating conditions, which is undesirable.